Harken's 40mm Zircon Double Block, Part No. 2192, has a maximum working load of 230 kg (or 500 lbs) and can accommodate lines up to 8 mm (or 5/16 in) in diameter. Its 40 mm (or 1 9/16 in) sheave is made of industrial ceramic ball bearings mounted inside caged races for optimal performance. These bearings are kept separated by cages to prevent friction and maximize efficiency, making this block the most efficient option for small boats from Harken. Available in both single and double blocks with or without beckets, the Zircon block helps trimmers quickly adjust sail shapes to changing conditions.